In semiconductor fabrication, various processes are monitored by collecting data and analyzing conditions within a semiconductor processing chamber. This is traditionally carried out using a window mounted, for example, on a side wall of the processing chamber. Prior Art FIG. 1 shows one example of a window 10 mounted on a side wall of a conventional processing chamber 12. As shown, the window 10 is recessed with respect to the side wall of the processing chamber 12.
While various processes are carried out within the processing chamber 12, byproducts in the form of polymer precursors and residue tend to accumulate on the window 10. This interferes with the collection of data and analysis of conditions within the processing chamber 12. To overcome this difficulty, a source of inert gas 14 is commonly used to channel an inert gas in front of the window 10 for removing the byproducts. In prior art processing chambers 12, Helium (He) is commonly used to clean the window 10.
While Helium is effective in removing polymer precursors from the window 10, difficulties do arise which result from use of such inert gas. For example, Helium tends to at least partially affect the process within the process chamber 12 by diluting and/or altering the gas composition within the processing chamber 12. As such, a flow rate of the Helium is kept to a minimum to prevent a large volume of the gas from being injected into the process chamber 12. In the end, the reduced flow rate of Helium is only partially effective in removing the byproducts from the window 10. To compensate for this deficiency, an inboard end of the recessed area has a conventional O-ring 13 to reduce exposure of the window 10 to the byproducts. Such O-ring 13, however, prevents the use of equipment commonly employed for analyzing wafers within the process chamber.
There is thus a need for a semiconductor processing chamber with optical window that effectively prevents the deposition of byproducts on the window while avoiding the alteration of the process gas composition within the processing chamber and allowing use of equipment to analyze wafers within the process chamber.
As mentioned earlier, the processes within the processing chamber are monitored by collecting data and analyzing conditions. Examples of equipment necessary for such collection and analysis include a lamp, a spectrometer, an optical fiber, and a lens. In use, the optical fiber has a first end aligned with the window with the lens positioned therebetween. A second end of the optical fiber is bifurcated for coupling to both the lamp and the spectrometer.
During operation, the lamp and the spectrometer work together to monitor a process such as deposition, etching, or cleaning by any one of the known optical endpoint detection methods. In one such method, light is reflected off of the wafer and thereafter viewed with the spectrometer. The spectrometer may be connected to a photodetector that converts light from the spectrometer to an electrical signal which is in turn amplified and monitored by a computer to determine a process endpoint or collecting other information.
A complication arises due to the need for directing the light and viewing the reflected light through a single window. In particular, some of the directed light reflects back from the window and tends to interfere with the ability of the spectrometer to receive the light reflected from the wafer within the processing chamber. This reflected light, or noise, prevents the spectrometer and the associated photodetector from delivering an electrical signal that is truly indicative of the light reflected from the wafer within the processing chamber.
There is thus a need for a semiconductor processing chamber that effectively employs a single window to direct light into the processing chamber and receive reflected light without noise for analysis purposes.